Investigation of the Effects of PACAP on the Composition of Tear and Endolymph Proteins

Abstract

Pituitary adenylate cyclase activating polypeptide (PACAP) is widely distributed in ocular tissues, including the lacrimal gland. PACAP has been shown to influence the activity of several exocrine glands, but its effects on the composition of the tear film are not known yet. Similarly, the presence of PACAP has already been shown in the inner ear, but it is not known whether PACAP influences the composition of the endolymph. The aim of the present study was to investigate whether systemic injection of PACAP has any modulatory effects on the protein composition of the tear film and endolymph using chip electrophoresis and mass spectrometry analysis. Tear and endolymph samples were collected from rats and chickens, respectively, at various time points after systemic injection of PACAP. Fluid samples were further processed for chip electrophoretic studies. No difference was found in the protein composition of the endolymph between control and PACAP-treated animals. In contrast, tear samples showed a marked difference after PACAP treatment. Proteins in the molecular range 50-70 kDa, which showed a different chip electropherogram profile in every PACAP-treated sample, were further analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. PACAP treatment induced a repression in certain keratins, while others were induced after PACAP injection. Furthermore, PACAP treatment decreased aldehyde dehydrogenase expression. The present study provides a base for further studies on the in vivo effects of PACAP on the composition of tear film. These investigations may have important clinical relevance because of the noninvasive sample collection, the correlation between tear proteins and ocular diseases, and the possible presence of biomarkers for both ophthalmological and systemic pathological conditions.

Pituitary adenylate cyclase activating polypeptide in the retina: focus on the retinoprotective effects

“…Intravitreal injection of PACAP induces hyperemia and mimicked the symptoms of ocular inflammation in the rabbit eye, indicating an involvement of PACAP in ocular inflammatory responses 33 . Systemic injection of PACAP has been shown to modify certain protein components of the rat tear film 53 …”

Pleiotropic and retinoprotective functions of PACAP

“…Intravitreal injection of PACAP induces hyperemia and mimics the symptoms of ocular inflammation in the rabbit eye, indicating the involvement of PACAP in ocular inflammatory responses (Wang et al 1995). Systemic injection of PACAP has been demonstrated to modify certain protein components of the rat tear film (Gaal et al 2008). Recently, a new recombinant PACAP-derived peptide has also been shown to promote corneal wound repair and lacrimal secretion (Ma et al 2015).…”

Pituitary Adenylate Cyclase-Activating Polypeptide in the Auditory System

“…Our research group examined the protein composition of chicken endolymph after PACAP38 treatment [ 8 ]. We treated 1-day-old chicken with intraperitoneal PACAP38 injection.…”

“…Then we removed the membranous labyrinth and the endolymph was squeezed to a sterile paper strip. Then we utilized microchip electrophoresis using protein 230 Plus LabChip Kit evaluated with Agilent 2100 Bioanalyzer System [ 8 ]. Endolymph, which fi lls the membranous labyrinth, is produced in the stria vascularis, it is rich in potassium and poor in sodium.…”

“…Thereafter, we discuss the functional changes in the inner ear related to PACAP. We summarize the effects of PACAP on the endolymph composition [ 8 ], on apoptosis in chicken inner ear cell cultures in vitro [ 9 ], and its effects on Ca 2+ -binding protein expression in hair cells [ 7 , 10 ].…”